U.S. patent application number 13/903225 was filed with the patent office on 2013-12-05 for radar apparatus and signal processing method.
This patent application is currently assigned to Fujitsu Ten Limited. The applicant listed for this patent is Fujitsu Ten Limited. Invention is credited to Masayuki KISHIDA, Takumi MORIUCHI.
Application Number | 20130321195 13/903225 |
Document ID | / |
Family ID | 49579739 |
Filed Date | 2013-12-05 |
United States Patent
Application |
20130321195 |
Kind Code |
A1 |
MORIUCHI; Takumi ; et
al. |
December 5, 2013 |
RADAR APPARATUS AND SIGNAL PROCESSING METHOD
Abstract
There is provided a radar apparatus. A first determining section
is configured to determine whether there exists a continuing
stationary target at a side of a lane in which a vehicle is
traveling. A second determining section is configured to determine
whether there exists a moving target in a specific range which is
in front of the vehicle and on an opposite side of the stationary
target with respect to a position of the vehicle. A changing
section is configured to change position information of the moving
target to a position obtained by folding back a specific position
which is the position of the moving target in the specific range
with the stationary target therebetween in a case where the
stationary target exists and the moving target exists in the
specific range. The changed position is used for deriving the
position information of the target.
Inventors: |
MORIUCHI; Takumi; (Kobe-shi,
JP) ; KISHIDA; Masayuki; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Fujitsu Ten Limited |
Kobe-shi |
|
JP |
|
|
Assignee: |
Fujitsu Ten Limited
Kobe-shi
JP
|
Family ID: |
49579739 |
Appl. No.: |
13/903225 |
Filed: |
May 28, 2013 |
Current U.S.
Class: |
342/70 |
Current CPC
Class: |
G01S 13/931 20130101;
G01S 2013/9325 20130101; G01S 13/52 20130101; G01S 2013/93185
20200101; G01S 2013/93271 20200101; G01S 7/354 20130101; G01S
2013/932 20200101; G01S 2013/93272 20200101; G01S 13/345 20130101;
G01S 13/536 20130101; G01S 2013/9321 20130101; G01S 2013/93274
20200101; G01S 2013/9319 20200101 |
Class at
Publication: |
342/70 |
International
Class: |
G01S 13/52 20060101
G01S013/52 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2012 |
JP |
2012-125050 |
Claims
1. A radar apparatus configured to radiate a transmission wave
relating to a frequency-modulated transmission signal, receive a
reflected wave of the transmission wave from a target as a
reception signal, and derive at least position information of the
target from the reception signal, the radar apparatus comprising: a
first determining section configured to determine whether there
exists a continuing stationary target at a side of a lane in which
a vehicle with the radar apparatus mounted thereon is traveling; a
second determining section configured to determine whether there
exists a moving target in a specific range which is in front of the
vehicle and on an opposite side of the stationary target with
respect to a position of the vehicle; and a changing section
configured to change position information of the moving target to a
position obtained by folding back a specific position which is the
position of the moving target in the specific range with the
stationary target therebetween in a case where the stationary
target exists and the moving target exists in the specific range,
wherein the position changed by the changing section is used for
deriving the position information of the target.
2. The radar system according to claim 1, wherein the changing
section changes the position information of the moving target to a
position substantially symmetrical to the specific position about a
line segment extending in a traveling direction of the vehicle and
including the position of the stationary target.
3. The radar system according to claim 1, wherein the second
determining section determines whether there exists at least one
stationary target between the position of the vehicle and the
specific position and in a predetermined range relative to the
specific position, and wherein the changing section changes the
position information of the moving target in a case where there
exists the at least one stationary target.
4. A signal processing method for a radar apparatus configured to
radiate a transmission wave relating to a frequency-modulated
transmission signal, receive a reflected wave of the transmission
wave from a target as a reception signal, and derive at least
position information of the target from the reception signal, the
signal processing method comprising: determining whether there
exists a continuing stationary target at a side of a lane in which
a vehicle with the radar apparatus mounted thereon is traveling;
determining whether there exists a moving target in a specific
range which is in front of the vehicle and on an opposite side of
the stationary target with respect to a position of the vehicle;
and changing position information of the moving target to a
position obtained by folding back a specific position which is the
position of the moving target in the specific range with the
stationary target therebetween in a case where the stationary
target exists and the moving target exists in the specific range,
wherein the position changed in the changing is used for deriving
the position information of the target.
Description
[0001] The disclosure of Japanese Patent Application No.
2012-125050 filed on May 31, 2012, including specification,
drawings and claims is incorporated herein by reference in its
entirety.
TECHNICAL FIELD
[0002] The present invention relates to signal processing in
deriving the position of a target.
BACKGROUND
[0003] According to the related art, a radar apparatus of a vehicle
outputs a transmission wave from the antenna of the radar
apparatus. If the output transmission wave is reflected from a
target and the reflected wave is received by the antenna, the radar
apparatus derives the position of the target relative to the
vehicle (the radar apparatus). The detailed process is as follows.
In the radar apparatus, a signal processing unit mixes a
transmission signal which corresponds to the transmission wave and
whose frequency varies with a predetermined period, and a reception
signal which corresponds to the reflected wave, thereby generating
a beat signal. Specifically, the predetermined period of the
transmission signal includes an UP section where the frequency
increases and a DOWN section where the frequency decreases, and the
signal processing unit generates a signal (hereinafter, referred to
as a "beat signal") based on the frequency difference between the
reception signal and the transmission signal (which is a beat
frequency) in each of the UP section and the DOWN section.
[0004] Next, the signal processing unit takes the Fast Fourier
Transform (FFT) of each beat signal, thereby generating signals of
different frequencies (hereinafter, referred to as "transformed
signals"), and detects signals exceeding a predetermined signal
level threshold as peak signals from the transformed signals. Then,
on the basis of information such as the signal levels and
frequencies of the peak signals, the signal processing unit pairs a
peak signal of the UP section corresponding to one target, and a
peak signal of the DOWN section corresponding to the same target,
thereby deriving pair data.
[0005] Next, on the basis of the pair data, the signal processing
unit derives a distance until the reflected wave reflected from the
target arrives a receiving antenna 14 of a radar apparatus 1
(hereinafter, referred to as a "longitudinal distance"). Also, the
signal processing unit derives the distance between the vehicle and
the target in a lateral direction relative to the traveling
direction of the vehicle (hereinafter, referred to as a "lateral
distance"). In other words, on the basis of the pair data, the
signal processing unit derives information on the position of the
target as seen from the vehicle. Further, the signal processing
unit derives a relative speed which is the speed of the target
relative to the running vehicle. As target categories based on
relative speeds, for example, there are stationary targets having
almost the same relative speed as the speed of the vehicle and
moving targets having relative speeds different from the speed of
the vehicle. Next, the radar apparatus outputs the derived
information such as the position of a moving target to a vehicle
control unit for controlling the operation of the vehicle. As a
result, the vehicle control unit performs necessary control on the
vehicle according to the position of the moving target and the like
output from the radar apparatus. Also, as a reference for
explaining a technology related to the present invention, there is
Patent Document 1. [0006] Patent Document 1: Japanese Patent
Application Publication No. 2009-133761
[0007] However, for example, in a case where the vehicle is
traveling at a place where stationary targets are derived in
relatively large numbers, like in a tunnel, the signal processing
unit of the radar apparatus cannot derive information such as the
origin positions of the targets. In other words, in a frequency
band where there are a number of peak signals corresponding to a
continuing stationary target like in a tunnel, pairing of peak
signals (hereinafter, referred to as "movement peak signals")
corresponding to a moving target may not be appropriately
performed. Specifically, without paring the movement peak signal of
the UP section and the movement peak signal of the DOWN section,
the movement peak signal of the UP section and a stationary peak
signal of the DOWN section may be paired, or a stationary peak
signal of the UP section and the movement peak signal of the DOWN
section may be paired. As a result, pair data based on the movement
peak signals may not be derived and thus information such as the
position of the moving target may not be derived.
[0008] Also, in a case where the signal level of a stationary peak
signal existing in the vicinity of the frequency of a movement peak
signal is higher than the signal level of the movement peak signal,
the movement peak signal may be included in the stationary peak
signal, and thus pairing of the movement peak signal of the UP
section and the movement peak signal of the DOWN section may not be
performed. As a result, pair data based on the movement peak
signals may not be derived and thus information such as the
position of the moving target may not be derived. As a result,
sometimes the vehicle control unit cannot perform necessary control
on the vehicle on the basis of information such as the position of
the moving target output from the radar apparatus.
SUMMARY
[0009] It is therefore an object of the present invention to derive
information on the accurate position of a moving target.
[0010] In order to achieve the above object, according to a first
aspect of the embodiments of the present invention, there is
provided a radar apparatus configured to radiate a transmission
wave relating to a frequency-modulated transmission signal, receive
a reflected wave of the transmission wave from a target as a
reception signal, and derive at least position information of the
target from the reception signal, the radar apparatus comprising: a
first determining section configured to determine whether there
exists a continuing stationary target at a side of a lane in which
a vehicle with the radar apparatus mounted thereon is traveling; a
second determining section configured to determine whether there
exists a moving target in a specific range which is in front of the
vehicle and on an opposite side of the stationary target with
respect to a position of the vehicle; and a changing section
configured to change position information of the moving target to a
position obtained by folding back a specific position which is the
position of the moving target in the specific range with the
stationary target therebetween in a case where the stationary
target exists and the moving target exists in the specific range,
wherein the position changed by the changing section is used for
deriving the position information of the target.
[0011] The changing section may change the position information of
the moving target to a position substantially symmetrical to the
specific position about a line segment extending in a traveling
direction of the vehicle and including the position of the
stationary target.
[0012] The second determining section may determine whether there
exists at least one stationary target between the position of the
vehicle and the specific position and in a predetermined range
relative to the specific position, and the changing section may
change the position information of the moving target in a case
where there exists the at least one stationary target.
[0013] In order to achieve the above object, according to a second
aspect of the embodiments of the present invention, there is
provided a signal processing method for a radar apparatus
configured to radiate a transmission wave relating to a
frequency-modulated transmission signal, receive a reflected wave
of the transmission wave from a target as a reception signal, and
derive at least position information of the target from the
reception signal, the signal processing method comprising:
determining whether there exists a continuing stationary target at
a side of a lane in which a vehicle with the radar apparatus
mounted thereon is traveling; determining whether there exists a
moving target in a specific range which is in front of the vehicle
and on an opposite side of the stationary target with respect to a
position of the vehicle; and changing position information of the
moving target to a position obtained by folding back a specific
position which is the position of the moving target in the specific
range with the stationary target therebetween in a case where the
stationary target exists and the moving target exists in the
specific range, wherein the position changed in the changing is
used for deriving the position information of the target.
[0014] According to the aspects of the present invention, the
position information of the moving target is set to a position
which is in front of the vehicle and is on the opposite side of the
stationary targets with respect to the specific position.
Therefore, it is possible to derive the accurate position
information of the moving target.
[0015] Also, according to the aspects of the present invention, the
position information of the moving target is changed to a position
which is substantially symmetrical to the specific position with
respect to the line segment extending in the traveling direction of
the vehicle and including the positions of the stationary targets.
Therefore, it is possible to derive the accurate position
information of the moving target existing at the position
symmetrical to the original position.
[0016] Further, according to the aspects of the present invention,
in the case where at least one stationary target exists, the
position information of the moving target is changed. Therefore, it
is possible to derive the accurate position information of the
moving target corresponding to a multi-path reflected wave.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In the accompanying drawings:
[0018] FIG. 1 is a general view of a vehicle.
[0019] FIG. 2 is a block diagram illustrating a vehicle control
system.
[0020] FIG. 3 is a view mainly illustrating the waveforms of a
transmission signal and a reception signal of a radar
apparatus.
[0021] FIG. 4 is a view mainly illustrating the scan range of a
radar apparatus mounted on a vehicle.
[0022] FIG. 5 is a view mainly illustrating the angles and
longitudinal distances of targets relative to the vehicle.
[0023] FIG. 6 is a view mainly illustrating the position of a
moving target based on a multi-path reflected wave.
[0024] FIG. 7 is a flow chart of a target data deriving
process.
[0025] FIG. 8 is another flow chart of the target data deriving
process.
[0026] FIG. 9 is a further flow chart of the target data deriving
process.
[0027] FIG. 10 is a flow chart of a position information changing
process.
[0028] FIG. 11 is a flow chart of a multi-path movement target
determining process.
[0029] FIG. 12 is another flow chart of the multi-path movement
target determining process.
[0030] FIG. 13 is a view illustrating a specific range in
determining a multi-path movement target.
[0031] FIG. 14 is a view illustrating setting of a reflecting
range.
[0032] FIG. 15 is a flow chart of a position changing process.
[0033] FIG. 16 is a view illustrating deriving of a lateral
distance difference.
[0034] FIG. 17 is a view illustrating changing of the position
information of a moving target.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0035] Hereinafter, an embodiment of the present invention will be
described with reference to the accompanying drawings. The
following embodiment is merely illustrative and the technical scope
of the present invention is not limited thereto.
First Embodiment
[0036] <1. Configuration>
[0037] <1-1. General View of Vehicle>
[0038] FIG. 1 is a general view of a vehicle 100. The vehicle 100
has a radar apparatus 1 which is included in a vehicle control
system 10 of the present embodiment, and a vehicle control device
2. The radar apparatus 1 is installed at a front portion of the
vehicle. The radar apparatus 1 performs scanning once to scan a
scan range SC, and derives the position information of a target
including the longitudinal distance and lateral distance of the
target relative to the vehicle 100. The lateral distance of the
target relative to the vehicle 100 corresponds to the angle of the
target relative to the vehicle 100. Also, the radar apparatus 1
derives the relative speed of the target to the speed of the
vehicle 100.
[0039] Although the radar apparatus 1 of FIG. 1 has been mounted on
a front portion of the vehicle, the mounting position of the radar
apparatus 1 on the vehicle 100 is not limited to the front portion.
The radar apparatus 1 may be mounted on any other portion such as a
rear portion of the vehicle 100 or a side mirror of the vehicle 100
where it is possible to derive the positions of targets.
[0040] The vehicle control device 2 is installed inside the vehicle
100, and is an electronic control unit (ECU) for controlling each
unit of the vehicle 100.
[0041] <1-2. Block Diagram of System>
[0042] FIG. 2 is a block diagram of the vehicle control system 10.
The vehicle control system 10 includes the radar apparatus 1 and
the vehicle control device 2. In the vehicle control system 10, the
radar apparatus 1 and the vehicle control device 2 are electrically
connected, and the vehicle control system 10 mainly outputs data of
targets (hereinafter, referred to as the "target data") derived by
the radar apparatus 1, to the vehicle control device 2. In other
words, the radar apparatus 1 outputs target data which are
information on the longitudinal distances, lateral distances, and
relative speeds of targets relative to the vehicle 100, to the
vehicle control device 2. Then, on the basis of the target data,
the vehicle control device 2 controls the operation of each unit of
the vehicle 100. Also, the vehicle control device 2 is electrically
connected to various sensors such as a vehicle speed sensor 40 and
a steering sensor 41 provided to the vehicle 100. Further, the
vehicle control device 2 is electrically connected to various units
such as a brake 50, a throttle 51, and an alarm unit 52 provided to
the vehicle 100. Furthermore, the vehicle speed sensor 40, the
steering sensor 41, the brake 50, the throttle 51, and the alarm
unit 52 are installed outside the vehicle control system 10.
[0043] The radar apparatus 1 derives the target data of an object
such as another vehicle which exists at the periphery of the
vehicle 100 with the radar apparatus 1. Specifically, the radar
apparatus 1 radiates a transmission wave relating to a
frequency-modulated transmission signal. If the transmission wave
is reflected from a target, the radar apparatus 1 receives the
reflected wave as a reception signal, and derives the target data
from the reception signal. Then, on the basis of the target data
derived by the radar apparatus 1, the vehicle control device 2
outputs various signals such as control signals for operating the
brake 50, adjusting the opening of the throttle 51, and reporting
an alarm of the alarm unit 52 to the user of the vehicle.
[0044] The radar apparatus 1 mainly includes a signal generating
unit 11, an oscillator 12, transmitting antennae 13, receiving
antennae 14, mixers 15, analog-to-digital (AD) converters 16, and a
signal processing unit 17.
[0045] The signal generating unit 11 generates a modulated signal
with a voltage changing, for example, in a triangular wave form, on
the basis of a control signal of a transmission control unit 107 to
be described below.
[0046] The oscillator 12 is a voltage control oscillator for
controlling an oscillation frequency by a voltage, and performs
frequency modulation on a signal in a predetermined frequency band
(for example, a signal in a frequency band having 76.5 GHz as the
center frequency) on the basis of the modulated signal generated by
the signal generating unit 11, and outputs the frequency-modulated
signal as the transmission signal to the transmitting antennae
13.
[0047] The transmitting antennae 13 output a transmission wave
relating to the transmission signal to the outside of the vehicle.
The radar apparatus 1 of the present embodiment includes two
transmitting antennae, that is, a transmitting antenna 13a and a
transmitting antenna 13b. Switching between the transmitting
antennae 13a and 13b is performed with a predetermined period by
switching of a switching unit 131, and the transmission wave is
continuously output from a transmitting antenna 13 connected to the
oscillator 12 to the outside of the vehicle.
[0048] The switching unit 131 is a switch for switching between the
transmitting antennae 13 to be connected to the oscillator 12, and
connects any one transmitting antenna of the transmitting antenna
13a and the transmitting antenna 13b to the oscillator 12 according
to a signal of the transmission control unit 107.
[0049] The receiving antennae 14 is a plurality of antennae for
receiving a reflected wave of a transmission wave, continuously
transmitted from a transmitting antenna 13, from a target. In the
present embodiment, there are provided four receiving antennae,
that is, a receiving antennae 14a (ch1), 14b (ch2), 14c (ch3), and
14d (ch4). The receiving antennae 14a to 14d are disposed at
regular intervals.
[0050] The mixers 15 are provided for the receiving antennae,
respectively. Each mixer 15 mixes a reception signal and a
transmission signal, thereby generating a beat signal which is a
difference signal between the transmission signal and the reception
signal and the transmission signal, and outputs the beat signal to
a corresponding AD converter 16.
[0051] The AD converter 16 samples the beat signal which is an
analog signal, at predetermined intervals, thereby deriving a
plurality of sample data items. Then, the AD converter 16 quantizes
the sample data items, thereby converting the beat signal which is
analog data, into digital data, and outputs the digital data to the
signal processing unit 17. Like the mixers 15, the AD converters 16
are also provided for the receiving antennae, respectively.
[0052] The signal processing unit 17 is a computer including a CPU
171 and a memory 172, and derives target data on the basis of the
beat signal output from the AD converter 16. Here, the signal
processing unit 17 derives a peak signal in the process of deriving
the target data from the beat signal. This peak signal has a
frequency depending on the channel of the reflected wave of the
transmission wave from the object to the antenna. For example, in a
case where a transmission wave radiated from the antennae is
reflected from different targets (different reflective points) of
one object (for example, a front vehicle traveling in front of the
vehicle 100), if a reflected wave from a target corresponding to a
reflective point of the front vehicle is directly received by the
antennae, without being reflected from any other reflective point,
the peak signal of the reflected wave (hereinafter, referred to as
the "direct wave") has one frequency. Also, if a reflected wave
from a target is further reflected from another reflective point,
and is received by the antennae, the peak signal of the reflected
wave (hereinafter, referred to as the "multi-path reflected wave")
has a frequency different from the frequency of the peak signal of
the direct wave. Further, a peak signal corresponding to a direct
wave has a frequency corresponding to the original point
information of a corresponding target; whereas a peak signal
corresponding to a multi-path reflected wave has a frequency
corresponding to position information different from the original
position of a corresponding target due to reflection of a
corresponding reflected wave from another target. Also, whether a
reflected wave will be a direct wave or a multi-path reflected wave
depends on the shape of a corresponding reflective point or the
surroundings of the vehicle (such as whether there exists any
obstacle).
[0053] Further, the signal processing unit 17 determines whether
there exists any continuing stationary target such as the inside
wall of a tunnel or a guardrail around the vehicle 100, on the
basis of the derived target data. In other words, the signal
processing unit 17 determines whether there exists any continuing
stationary target (for example, a stationary target continuing for
a distance of 40 m or more) at a side of a lane in which the
vehicle 100 is traveling. This is a process for determining whether
the surroundings of the traveling vehicle 100 are circumstances in
which a multi-path reflected wave may occur. In order to determine
whether there exists any continuing stationary target, the signal
processing unit 17 may determine whether the actual length of a
continuing stationary target is a predetermined value or more, or
may determine whether the number or density of stationary targets
in a predetermined distance range is a predetermined value or
more.
[0054] Then, the signal processing unit 17 determines whether there
exists any moving target such as a vehicle in a specific range on
the opposite side of the inside wall of a tunnel, a guardrail, or
the like with respect to the position of the vehicle 100. In other
words, the signal processing unit 17 determines whether there
exists any moving target in the specific range on the opposite side
of a continuing stationary target with respect to the position of
the vehicle 100 in front of the vehicle 100. This is a process for
determining whether there exists any moving target based on a
multi-path reflected wave in front of the vehicle 100. Here, the
specific range on the opposite side of a stationary target with
respect to the position of the vehicle 100 means the predetermined
range on the opposite side of a continuing stationary target with
respect to the position of the vehicle 100.
[0055] In a case where the surroundings of the vehicle 100 are
circumstances in which a multi-path reflected wave may occur like
in a tunnel, and there exists a moving target in the specific
range, the signal processing unit 17 changes the position
information of the moving target from the position of the moving
target existing in the specific range to another position with the
inside wall of a tunnel, a guardrail, or the like therebetween. In
other words, in the case where there exists a continuing stationary
target and there exists a moving target in the specific range, the
signal processing unit 17 changes the position information of the
moving target to a position obtained by folding back a specific
position which is the position of the moving target in the specific
range with the continuing stationary target therebetween. This is a
process for changing the position information of the moving target
based on the multi-path reflected wave to the original position of
the moving target. In this way, it is possible to derive the
accurate position information of the moving target. Here, the
position obtained by folding back the specific position with the
continuing stationary target therebetween means a position on the
opposite side of the specific position with respect to the
stationary target.
[0056] The CPU 171 performs various arithmetic processes on the
basis of various programs recorded in the memory 172. For example,
the signal processing unit 17 performs a process of changing the
position information of the moving target from the specific
position to another position with the continuing stationary target
therebetween.
[0057] The memory 172 stores programs for performing various
arithmetic processes to be executed by the CPU 171, and so on.
Also, the memory 172 stores information of a plurality of target
data items derived by the signal processing unit 17. For example,
the memory 172 stores target data (the longitudinal distances,
lateral distances, and relative speeds of targets) derived in the
past scanning and the current scanning. Further, the memory 172
stores the state of a flag (a reflection target flag to be
described below) representing whether a moving target is a target
based on a multi-path reflected wave as will be described
below.
[0058] The transmission control unit 107 is connected to the signal
processing unit 17, and outputs a control signal to the signal
generating unit 11 for generating a modulated signal, on the basis
of a signal from the signal processing unit 17. Also, on the basis
of a signal from the signal processing unit 17, the transmission
control unit 107 outputs a control signal to the switching unit 131
for connecting the oscillator 12 to any one transmitting antenna of
the transmitting antenna 13a and the transmitting antenna 13b.
[0059] The vehicle control device 2 controls the operation of each
unit of the vehicle 100. In other words, the vehicle control device
2 acquires information from various sensors such as the vehicle
speed sensor 40 and the steering sensor 41. Then, on the basis of
the information acquired from the various sensors and target data
acquired from the signal processing unit 17 of the radar apparatus
1, the vehicle control device 2 operates various units such as the
brake 50, the throttle 51, and the alarm unit 52 to control the
motion of the vehicle 100. An example of the control of the vehicle
control device 2 on the vehicle is as follows.
[0060] The vehicle control device 2 performs control such that the
vehicle 100 follows a front vehicle (for example, a front vehicle
200 shown in FIG. 4) traveling in front of the vehicle 100 in the
lane in which the vehicle 100 is traveling (for example, a lane ro1
shown in FIG. 4 to be described below). Specifically, the vehicle
control device 2 controls at least one of the brake 50 and the
throttle 51 according to the traveling of the vehicle 100, thereby
performing control such that the vehicle 100 follows the front
vehicle 200 with a predetermined distance between the vehicle 100
and the front vehicle 200. An example of this control is adaptive
cruise control (ACC).
[0061] Also, another example of the control of the vehicle control
device 2 on the vehicle is as follows. In a case where there is a
danger of a crash, the vehicle control device 2 controls the alarm
unit 52 such that the alarm unit displays a warning, and controls
the brake 50 such that the speed of the vehicle 100 is reduced.
Further, the vehicle control device 2 performs control such that an
occupant is fixed to the seat by a seat belt during a crash so as
to brace for the impact or a headrest is fixed to reduce damage to
the body of the occupant. An example of this control is a pre-crash
safety system (PCS). Also, the following description will be made
on the premise of the ACC for making the vehicle 100 follow the
front vehicle 200.
[0062] The vehicle speed sensor 40 outputs a signal according to
the speed of the vehicle 100 on the basis of the number of
revolutions of the axle of the vehicle 100. On the basis of the
signal from the vehicle speed sensor 40, the vehicle control device
2 acquires the current speed of the vehicle.
[0063] The steering sensor 41 senses the rotation angle of a
steering wheel according to the operation of the driver of the
vehicle 100, and transmits the angle information of the vehicle 100
to the vehicle control device 2.
[0064] The brake 50 reduces the speed of the vehicle 100 according
to the operation of the driver of the vehicle 100. Also, the brake
50 reduces the speed of the vehicle 100 according to the control of
the vehicle control device 2. For example, the brake 50 reduces the
speed of the vehicle 100 to maintain the distance between the
vehicle 100 and the front vehicle 200 at a predetermined
distance.
[0065] The throttle 51 reduces the speed of the vehicle 100
according to the operation of the driver of the vehicle 100. Also,
the throttle 51 reduces the speed of the vehicle 100 according to
the control of the vehicle control device 2. For example, the
throttle 51 reduces the speed of the vehicle 100 to maintain the
distance between the vehicle 100 and the front vehicle 200 at a
predetermined distance.
[0066] The alarm unit 52 operates in response to a signal from the
vehicle control device 2. For example, in a case where there is a
possibility of a crash of the vehicle 100 and the front vehicle
200, the alarm unit 52 outputs an alarm to the driver of the
vehicle 100 against the crash.
[0067] <2. Signal Processing of FM-CW>
[0068] Now, as an example of a signal processing scheme in which
the radar apparatus 1 derives the position of a target, a frequency
modulated continuous wave (FM-CW) scheme will be described.
Although the FM-CW scheme will be described as an example in the
present embodiment, the present invention is not limited to the
FM-CW scheme, but may be applied to any scheme of combining a
plurality of sections, such as an UP section in which the frequency
of a transmission signal increases, and a DOWN section in which the
frequency of a transmission signal decreases, thereby deriving a
target.
[0069] Also, in the following equations and FIG. 3, the reference
symbols of FM-CW signals and beat frequencies are as follow. A
symbol fr denotes a distance frequency, a symbol fd denotes a speed
frequency, a symbol fo denotes the center frequency of a
transmission wave, a symbol AF denotes a frequency shift width, a
symbol fm denotes the repetition frequency of a modulated wave, a
symbol c denotes a light speed (the speed of an electric wave), a
symbol T denotes the round-trip time of the electric wave between
the vehicle 100 and a target, a symbol fs denotes a transmission
(reception) frequency, a symbol fb denotes a beat frequency, a
symbol R denotes a longitudinal distance, a symbol V denotes a
relative speed, a symbol fup denotes the distance frequency of an
UP section, a symbol fdn denotes the distance frequency of a DOWN
section, a symbol .theta.m denotes the angle of the target, a
symbol .theta.up denotes an angle corresponding to the beat signal
of the UP section, and a symbol .theta.dn denotes an angle
corresponding to the beat signal of the DOWN section.
[0070] FIG. 3 is a view mainly illustrating a transmission signal
and reception signal of the radar apparatus 1. The upper view of
FIG. 3 shows the signal waveforms of a FM-CW transmission signal
and a FM-CW reception signal. The lower view of FIG. 3 shows beat
frequencies generated by the frequency difference between the
transmission signal and the reception signal. In the upper view of
FIG. 3, the horizontal axis represents time (ms), and the vertical
axis represents frequency (GHz). The transmission signal shown by a
solid line in the upper view of FIG. 3 has the characteristic that
the frequency changes with a predetermined period, and has UP
sections where the frequency increases from a predetermined lower
frequency to a predetermined upper frequency, and DOWN sections
where the frequency decreases from the predetermined upper
frequency to the predetermined lower frequency. In other words, the
transmission signal periodically changes between the predetermined
lower frequency and the predetermined upper frequency. If the
transmission wave is output from a transmitting antenna 13 and is
reflected from a target, a receiving antenna 14 receives the
reflected wave as a reception signal. The reception signal is as
shown by a broken line in FIG. 3. Similarly to the transmission
signal, the reception signal also has UP sections and DOWN
sections.
[0071] Also, according to the longitudinal distance between the
vehicle 100 and the target, the reception signal has a time delay T
(=2R/c) relative to the transmission signal. Further, in a case
where there is a speed difference between the vehicle 100 and the
target, with respect to the transmission signal, the reception
signal shifts in parallel along the axis of the frequency fs. This
Doppler shift amount becomes fd.
[0072] In the lower view of FIG. 3, the horizontal axis represents
time (ms), and the vertical axis represents frequency (KHz). The
lower view of FIG. 3 shows beat frequencies representing the
frequency difference between the transmission signal and the
reception signal in each UP section, and the frequency difference
between the transmission signal and the reception signal in each
DOWN section.
[0073] Here, the longitudinal distance of the target relative to
the vehicle 100 is derived by Equation 1, and the relative speed of
the target relative to the vehicle 100 is derived by Equation 2.
Also, the angle of the target relative to the vehicle 100 is
derived by Equation 3. Then, from information on the angle derived
by Equation 3 and the longitudinal distance of the target, the
lateral distance of the target relative to the vehicle 100 is
derived by an operation using a trigonometric function.
R = ( fup + fdn ) c 2 .times. ( 4 .times. .DELTA. F .times. fm ) [
EQUATION 1 ] V = ( fup - fdn ) c 2 .times. ( 4 .times. .DELTA. F
.times. fm ) [ EQUATION 2 ] .theta. m = .theta. up + .theta. dn 2 [
EQUATION 3 ] ##EQU00001##
[0074] <3. Derivation of Position Information of Target Based on
Reflected Wave>
[0075] <3-1. Scan Range>
[0076] Now, a moving target deriving process of the signal
processing unit 17 will be described with reference to FIGS. 4 to
9. FIG. 4 is a view mainly illustrating the scan range SC of the
radar apparatus 1 mounted on the vehicle 100. Also, FIG. 4 shows
the vehicle 100 traveling in the lane ro1, the front vehicle 200
traveling in front of the vehicle 100 in the same lane ro1 as that
of the vehicle 100, and a shelter Re located on the left side of
the lane ro1 in which the vehicle 100 is traveling. Here, the front
vehicle 200 is a moving target to be derived by the signal
processing unit 17 of the radar apparatus 1, and becomes, for
example, an object to be followed in the ACC of the vehicle control
device 2. Also, the shelter Re is, for example, the inside wall of
a tunnel or a guardrail, and is a continuing stationary target to
be derived by the signal processing unit 17.
[0077] The transmission wave is radiated from the radar apparatus 1
over the scan range SC including a portion of the lane ro1
including the front vehicle 200, a portion of the shelter Re, and a
portion of a neighboring lane ro2 next to the lane ro1. Then, the
radar apparatus 1 receives reflected waves from the front vehicle
200 and the shelter Re by the receiving antennae 14. Here, since
there is the shelter Re, the scan range SC includes a sheltered
area Ns is an area where the transmission wave does not reach.
Therefore, the signal processing unit 17 does not originally derive
the data of a target in the sheltered area Ns. Like this, the radar
apparatus 1 performs scanning once, thereby receiving reflected
waves from a moving target like the front vehicle 200 and a
stationary target like the shelter Re by the receiving antennae 14,
and derives target data including the position information and
relative speed of each target.
[0078] <3-2. Angle and Longitudinal Distance of Target>
[0079] FIG. 5 is a view mainly illustrating the angle and
longitudinal distance of each target relative to the vehicle 100.
Also, FIG. 5 shows a moving target pa and a moving target pb
corresponding to a plurality of reflective points of the rear
bumper of the front vehicle 200, and a stationary target rp
corresponding to one reflective point of the shelter Re. First, the
angle of each target will be described. For example, in a case
where the angle of a target, being directly in front of the vehicle
100, relative to the vehicle 100 is set to 0 degree, the angle of
the moving target pa existing directly in front of the vehicle 100
becomes 0 degree, the angle of the stationary target rp becomes an
angle .theta.a, and the angle of the moving target pb becomes an
angle .theta.b larger than the angle .theta.a. The signal
processing unit 17 derives the angle of each target on the basis of
the reflected wave of the corresponding target. Here, with respect
to the moving target pb, an angle different from the original angle
is derived for the following reason. In other words, the
transmission wave radiated from the transmitting antennae 13 is
reflected from the moving target pb and the reflected wave is
reflected from a reflective point mp of the shelter Re, whereby the
multi-path reflected wave is received by the receiving antennae 14
and the moving target pb is derived from the multi-path reflected
wave. For this reason, the signal processing unit 17 derives the
angle .theta.b corresponding to the position of the reflective
point mp as the angle of the moving target pb.
[0080] Also, the lateral distance of each moving target or
stationary target is derived by an operation of a trigonometric
function using the angle and longitudinal distance of the
corresponding target. For example, the lateral distance of the
stationary target rp is derived by an operation of a trigonometric
function using the angle .theta.a and a longitudinal distance L3 to
be described below.
[0081] Now, the longitudinal distance of each target will be
described. The signal processing unit 17 derives the longitudinal
distance of each of the moving target pa, the moving target pb, and
the stationary target rp relative to the vehicle 100 on the basis
of the reflected wave of the corresponding target. As shown in FIG.
5, the longitudinal distances of the moving target pa, the moving
target pb, and the stationary target rp relative to the vehicle 100
are L1, L2, and L3, respectively. Here, with respect to the moving
target pb, a distance different from the original longitudinal
distance is derived for the following reason. In other words, the
transmission wave radiated from the transmitting antennae 13 of the
radar apparatus 1 is reflected from the moving target pb and the
reflected wave is reflected from the reflective point mp of the
shelter Re, whereby the multi-path reflected wave is received by
the receiving antennae 14 and the moving target pb is derived from
the multi-path reflected wave. For this reason, the signal
processing unit 17 derives the longitudinal distance L2, which is
the sum of a distance from the moving target pb to the reflective
point mp and a distance from the reflective point mp to the vehicle
100, as the longitudinal distance of the moving target pb. However,
the position (angle and longitudinal distance) of the moving target
pb derived by the signal processing unit 17 becomes a position
corresponding to a moving target pc (to be described below with
reference to FIG. 6), not the original position of the moving
target pb.
[0082] <3-3. Position of Target of Multi-Path Reflected
Wave>
[0083] FIG. 6 is a view mainly illustrating the position of the
moving target pc based on the multi-path reflected wave. Also, FIG.
6 shows the moving target pc which the signal processing unit 17 of
the radar apparatus 1 derives on the basis of the multi-path
reflected wave from the moving target pb of FIG. 5 described above.
The position of the moving target pc is as follows. In other word,
the angle of the moving target pc is the same angle .theta.b as
that of the reflective point mp, and the longitudinal distance of
the moving target pc is the longitudinal distance L2. Further, as
the lateral distance of the moving target pc, a lateral distance S2
is derived by an operation of a trigonometric function using the
angle .theta.b and the longitudinal distance L2. Further, the
lateral distance of the stationary target rp becomes a lateral
distance S3 by an operation of a trigonometric function using the
angle .theta.a and the longitudinal distance L3. Furthermore, the
position of the moving target pc is in the range of the sheltered
area Ns separated by the shelter Re, where the target is not
originally derived.
[0084] With reference to FIG. 6, one stationary target rp
corresponding to one reflective point of the shelter Re has been
described as an example. However, from the shelter Re placed in the
scan range SC of the radar apparatus 1, with respect to the
transmission wave from the transmitting antennae 13 of the radar
apparatus 1, a plurality of reflected waves is received from a
plurality of reflective points of the shelter Re by the receiving
antennae 14. Then, in a case where the frequencies of a plurality
of stationary peak signals corresponding to the plurality of
reflected waves exist in the vicinity of the frequency of a peak
signal (hereinafter, referred to as a "movement direct peak
signal") corresponding to the direct wave from the moving target
pa, for example, if the signal levels of the stationary peak
signals are higher than the signal level of the movement direct
peak signal, the movement direct peak signal may be included in the
stationary peak signals such that the pair data of the movement
direct peak signal cannot be derived.
[0085] Also, even in a case where the pair data of a peak signal
(hereinafter, referred to as a "movement indirect peak signal")
corresponding to the multi-path reflected wave from the moving
target pb is derived, position information different from the
original point information is derived. Therefore, the signal
processing unit 17 of the radar apparatus 1 cannot derive the
accurate position information of the moving target corresponding to
the front vehicle 200 and thus the vehicle control device 2 cannot
make the vehicle 100 follow the front vehicle 200 on the basis of
the accurate position information.
[0086] In a case where the vehicle 100 is traveling at a place like
in a tunnel, even if it is impossible to derive pair data based on
the movement direct peak signal of one target, pair data based on
the corresponding target may be derived. In a case where the number
of stationary peak signals in the vicinity of the frequency of the
movement indirect peak signal in one process of a plurality of
target deriving processes of the radar apparatus 1 is smaller than
those in the other processes as the surroundings of the vehicle 100
change with time, the movement indirect peak signal may be detected
and the pair data of the movement indirect peak signal may be
derived.
[0087] Also, even in a case where there is a plurality of
stationary peak signals in the vicinity of the frequency of the
movement indirect peak signal, if the signal level of the movement
indirect peak signal is higher than the signal levels of the
stationary peak signals, the movement indirect peak signal may be
detected and the pair data based on the movement indirect peak
signal may be derived. As a result, even in a case where it is
impossible to derive the moving target based on the pair data of
the movement direct peak signal, the moving target based on the
pair data of the movement indirect peak signal may be derived. For
this reason, the position information of the moving target based on
the pair data of the movement indirect peak signal is used to
perform the process of deriving the original position of the moving
target. Hereinafter, the outline of the target data deriving
process of the signal processing unit 17 will be described, and
then a process of changing the position information of the moving
target based on the pair data of the movement indirect peak signal,
that is, the moving target based on the multi-path reflected wave
will be described in detail.
[0088] <4. Process Flow Chart>
[0089] <4-1. Entire Process>
[0090] FIGS. 7 to 9 are flow charts of the target data deriving
process. As shown in FIG. 7, first, in STEP S101, the transmitting
antennae 13 outputs a transmission wave corresponding to a
transmission signal output from the oscillator 12 to the outside of
the vehicle 100.
[0091] Also, in a case where one UP section and one DOWN section of
the transmission signal constitute one period, the transmitting
antennae 13 outputs the transmission wave corresponding to the
first period from one transmitting antenna 13a to the outside of
the vehicle, and outputs the transmission wave corresponding to the
second period from the other transmitting antenna 13b to the
outside of the vehicle.
[0092] If the transmission wave is reflected from a target, in STEP
S102, the receiving antennae 14 receive the reflected waves (the
direct wave and the multi-path reflected wave).
[0093] Next, in STEP S103, the mixers 15 mix reception signals
corresponding to the reflected waves received by the receiving
antennae 14 with the transmission signal, thereby generating beat
signals which are differences between the transmission signal and
the reception signals.
[0094] Then, in STEP S104, the AD converters 16 covert the beat
signals which are analog signals into digital data.
[0095] Subsequently, in STEP S105, the signal processing unit 17
performs FFT on the beat signals of the digital data, thereby
generating the transformed signals.
[0096] Next, as shown in FIG. 8, in STEP S106, from the transformed
signals, the signal processing unit 17 derives transformed signals
exceeding a predetermined threshold value as peak signals.
[0097] In STEP S107, the signal processing unit 17 performs an
angle computing process on the basis of the peak signals in each of
the UP section and the DOWN section. Specifically, the signal
processing unit 17 derives the angle of the target according to a
predetermined angle deriving process algorithm. For example, the
angle deriving process algorithm is Estimation of Signal Parameters
via Rotational Invariance Techniques (ESPRIT), and the eigenvalue,
eigenvector, and the like of a correlation matrix is computed from
information on the phase differences between the reception signals
of the receiving antennae 14a to 14d, and an angle .theta.up
corresponding to the peak signal of the UP section and an angle
.theta.dn corresponding to the peak signal of the DOWN section are
derived. Further, on the basis of the angles of the peak signals of
the UP section and the DOWN section, the angle of the target data
is derived by the above Equation 3.
[0098] Next, in STEP S108, the signal processing unit 17 pairs the
peak signals of the UP section and the DOWN section, and derives
the longitudinal distance and relative speed of the target relative
to the vehicle 100 on the basis of the above Equations 1 and 2.
[0099] The signal processing unit 17 performs a process of
determining whether there is a temporarily continuing relation
between the pair data (hereinafter, referred to as "current pair
data") obtained by the current target deriving process and data
(hereinafter, referred to as "predicted pair data") obtained by
predicting the current pair data on the basis of the target data
derived by the past target deriving process. Then, in a case where
there is a temporarily continuing relation between them, a
filtering process is performed between the current pair data and
the predicted pair data, and the filtered pair data (hereinafter,
referred to as "past corresponding pair data") as the target data
of the current scanning. Here, the case where there is a
temporarily continuing relation between the current pair data and
the predicted pair data is, for example, a case where each of the
values of the differences in the longitudinal distance, lateral
distance, and relative speed between the current pair data and the
predicted pair data is a predetermined value or less. Further, in
the case where there is a temporarily continuing relation between
the current pair data and the predicted pair data, with respect to
the longitudinal distances, the signal processing unit 17 assigns a
weight of 0.5 to the longitudinal distance of the predicted pair
data, and assigns a weight of 0.5 to the longitudinal distance of
the current pair data. Then, the signal processing unit 17 derives
the sum of the weighted values as the longitudinal distance of the
past corresponding pair data of the current scanning. Similarly,
even with respect to the relative speeds and the angles, a
filtering process is performed.
[0100] Meanwhile, in a case where any one of the values of the
differences in the longitudinal distance, lateral distance, and
relative speed between the current pair data and the predicted pair
data is greater than the predetermined value, the signal processing
unit 17 determines that there is no temporarily continuing relation
between the current pair data and the predicted pair data. Then,
the pair data determined as having no continuity like that becomes
data (hereinafter, referred to as "new pair data" derived for the
first time in the current target deriving process. The distance,
relative speed, angle, and signal level of the new pair data
becomes the distance, relative speed, angle, and signal level of
one target data item in the current target data deriving process.
In STEP S109, the signal processing unit 17 performs the
determining process and the filtering process as described above,
thereby deriving the longitudinal distance, lateral distance, and
relative speed of the target data in one target deriving process.
Also, in the process of STEP S109, it is determined whether the
kind of the target derived by the signal processing unit 17 is a
moving target or a stationary target.
[0101] Next, in STEP S110, on the target data derived in the
determining process of STEP S109, the signal processing unit 17
performs a multiple-stationary target determining process of
determining whether there exists the inside wall of any tunnel, any
guardrail, or the like around the vehicle 100. In other words, the
signal processing unit 17 determines whether there exists a
continuing stationary target (for example, a stationary target
continuing for a distance of 40 m or more) at a side of the lane
ro1 in which the vehicle 100 is traveling. Specifically, for
example, the signal processing unit 17 determines whether the
number of times of scanning, in each of which the peak signals
derived in the FFT process of STEP S105 includes more than 80 peak
signals corresponding to stationary targets, of a plurality of
times of scanning exceeds a predetermined number of times. Then, in
a case where the number of times of that scanning exceeds the
predetermined number of times, the signal processing unit 17
determines that the determination condition is satisfied. This is a
process for determining whether the circumferences in which the
vehicle 100 is traveling are circumferences where a multi-path
reflected wave may occur.
[0102] Next, as shown in FIG. 9, in a case of determining that
there exists a continuing stationary target at a side of the lane
ro1 in which the vehicle 100 is traveling (Yes in STEP S111), the
signal processing unit 17 proceeds to the process of STEP S112.
Meanwhile, in a case of determining that there exists no continuing
stationary target at a side of the traveling direction of the
vehicle 100 (No in STEP S111), the signal processing unit 17
proceeds to the process of STEP S113.
[0103] In STEP S112, on the base of the target data derived in the
determining process of the STEP S109, the signal processing unit 17
determines whether there exists any moving target based on a
multi-path reflected wave. In a case where there exists a moving
target based on a multi-path reflected wave, the signal processing
unit 17 performs a process of changing the position information of
the corresponding moving target. The process contents of this
process of changing the position information of the moving target
will be described below in detail.
[0104] Next, in STEP S113, the signal processing unit 17 performs a
classifying process on the target data derived in STEP S109.
Specifically, the signal processing unit 17 performs the following
classification on each item of the target data. In a case where one
moving target satisfies a predetermined condition for an object of
a leading vehicle traveling in front of the vehicle 100, the signal
processing unit 17 classifies the corresponding moving target as an
object of the leading vehicle. Meanwhile, in a case where one
moving target satisfies a predetermined condition for an object of
the ACC, the signal processing unit 17 classifies the corresponding
moving target as an ACC object.
[0105] Here, an example of the predetermined condition for
classification as the leading vehicle is as follows. A moving
target exiting in a range in which the longitudinal distance from
the position of the radar apparatus 1 of the vehicle 100 is less
than 120 m, the lateral distance in the left direction from the
position of the radar apparatus 1 of the vehicle 100 is less 5.4 m,
and the lateral distance in the right direction from the position
of the radar apparatus 1 of the vehicle 100 is less 5.4 m (for
example, a leading-vehicle determination range pr shown in FIG. 13
to be described below) is classified as an object of the leading
vehicle. Also, an example of the predetermined condition for
classification as the ACC object is as follows. A moving target
existing in a range in which the longitudinal distance from the
position of the radar apparatus 1 of the vehicle 100 is less than
120 m, the lateral distance in the left direction from the position
of the radar apparatus 1 of the vehicle 100 is less than 1.8 mm,
and the lateral distance in the right direction from the position
of the radar apparatus 1 of the vehicle 100 is less 1.8 m (for
example, the lane ro1 in which the vehicle 100 is traveling), the
corresponding moving target is classified as the ACC object.
[0106] Next, in STEP S114, the signal processing unit 17 performs a
process of combining target data items corresponding to each
target, on the plurality of target data items. For example, in a
case where a transmission wave is radiated from the transmitting
antennae 13 of the radar apparatus 1 and the transmission wave is
reflected from the front vehicle 200, a plurality of reflected
waves are received by the receiving antennae 14. In other words,
the reflected waves from a plurality of reflective points arrive
the receiving antennae 14. As a result, the signal processing unit
17 derives a plurality of target data items different in the
position information, on the basis of the reflected waves,
respectively. However, since the plurality of target data items is
originally the target data of the front vehicle 200 which is one
target, the individual target data items need to be combined and be
treated as one target data item. For this reason, the process of
STEP S114 is performed. In other words, if the relative speeds of a
plurality of target data items are substantially the same, and the
longitudinal distances and lateral distances of the target data
items are in the predetermined ranges, the signal processing unit
17 considers the plurality of target data items as the data of the
same target, and performs a process of combining the plurality of
target data items as one target data item. If the changed position
information of the moving target in which the position information
has been changed by the position information changing process of
the moving target is derived by the process of STEP S112, it is
possible to derive more accurate position information since the
moving target of which the position information has been changed is
added to the plurality of data items when combining the plurality
of target data items as one target data item. In other words, when
a plurality of target data items corresponding to one object are
derived, by deriving a value obtained by averaging the position
information of the plurality of target data items in which the
moving target of which the position information is changed is added
to the target data items to be combined (for example, an average
value of the longitudinal distances of the plurality of target data
items to which the changed moving target is added and an average
value of the lateral distances of the plurality of target data
items to which the changed moving target is added), it is possible
to derive the accurate position information of the one object, as
compared with a case where a value obtained by averaging the
position information without adding the moving target in which the
position information is changed.
[0107] Next, the signal processing unit 17 outputs a high-priority
target data item of the target data items combined in STEP S114 to
the vehicle control device 2 in STEP S115, and terminates the
target data deriving process. Here, the high-priority target data
item is, for example, a target data item having a relative speed
higher than those of the other target data items, a target data
item having a longitudinal distance and a lateral distance smaller
than those of the other target data items, or the like.
[0108] <4-2. Position Information Changing Process>
[0109] Next, the position information changing process of STEP S112
of FIG. 9 will be described in detail with reference to FIG. 10.
FIG. 10 is a flow chart of the position information changing
process. Referring to FIG. 10, in STEP S201, the signal processing
unit 17 determines whether the moving target derived in the
determining process of STEP S109 of FIG. 9 is a moving target
existing on the neighboring lane ro2 shown in FIG. 4 and so on and
overtaking the vehicle 100. Specifically, in a case where the
target which is the object of the determination is a moving target
corresponding to new pair data, the longitudinal distance of
corresponding target data is less than 20 m, and the lateral
distance of the corresponding target data is 1.8 m or more, the
signal processing unit 17 determines that the corresponding moving
target is a moving target existing on the neighboring lane ro2 and
overtaking the vehicle 100 (hereinafter, referred to as an
"overtaking target"). This is a process for preventing an
overtaking target traveling in the neighboring lane ro2 from being
erroneously determined as a moving target based on a multi-path
reflected wave.
[0110] Then, in a case where the target which is the object of the
determination of STEP S201 is an overtaking target (Yes in STEP
S202), the signal processing unit 17 proceeds to the process of
STEP S203. Meanwhile, in a case where the target which is the
object of the determination of STEP S201 is not an overtaking
target (No in STEP S202), the signal processing unit 17 proceeds to
the process of STEP S205.
[0111] In STEP S203, on the basis of the target data of the target
derived in the determining process of STEP S109, the signal
processing unit 17 determines whether there exists any moving
target such as a vehicle in a predetermined range separated by the
inside wall of a tunnel, a guardrail, or the like from the position
of the vehicle 100. In other words, the signal processing unit 17
determines whether there exists any moving target in a specific
range in front of the vehicle 100 and on the opposite side of a
continuing stationary target with respect to the position of the
vehicle 100. This is a process for determining whether there exists
a moving target based on a multi-path reflected wave in front of
the vehicle 100. This multi-path movement target determining
process will be described below in detail.
[0112] Next, in STEP S204, the signal processing unit 17 changes
the position information of the moving target from a specific
position to another position with the inside wall of the tunnel,
the guardrail, or the like therebetween. In other words, in a case
where a continuing stationary target exists, and the moving target
exists in the specific range, the signal processing unit 17 changes
the position information of the moving target to a position
obtained by folding back the specific position with the continuing
stationary target therebetween. This is a process for changing the
position information of the moving target based on the multi-path
reflected wave to the original position of the moving target. In
this way, it is possible to derive the accurate position
information of the moving target.
[0113] Then, if determining that the process on all of the moving
target data derived in the determining that the process of STEP
S109 has been terminated (Yes in STEP S205), the signal processing
unit 17 terminates the position information changing process.
Meanwhile, if determining that the process on all of the moving
target data has not been terminated (No in STEP S205), the signal
processing unit 17 returns to the process of STEP S201 and
continues the position information changing process.
[0114] <4-3. Multi-Path Movement Target Determining
Process>
[0115] Now, the multi-path movement target determining process of
STEP S203 will be described with reference to FIGS. 11 to 13. FIGS.
11 and 12 are flow charts of the multi-path movement target
determining process. This process to be described now is a process
for deriving each moving target based on a multi-path reflected
wave.
[0116] In FIG. 11, in a case where a plurality of moving targets
has been derived in the determining process of STEP S109, in STEP
S301, the signal processing unit 17 selects one moving target.
[0117] Next, in STEP S302, the signal processing unit 17 determines
whether the moving target derived in the current target deriving
process has been classified as an object of the leading vehicle in
the classifying process of STEP S113 of the previous target
deriving process. In other words, the signal processing unit 17
determines whether the moving target has been classified as an
object of the leading vehicle in the classifying process of the
previous target deriving process, with respect to the target data
of the past corresponding pair data derived in the current target
deriving process. Then, in a case of determining that the moving
target has been classified as an object of the leading vehicle (Yes
in STEP S302), the signal processing unit 17 proceeds to the
process of STEP S303. Meanwhile, in a case of determining that the
moving target has not been classified as an object of the leading
vehicle (No in STEP S302), the signal processing unit 17 proceeds
to the process of STEP S309 to be described below.
[0118] In STEP S303, the signal processing unit 17 determines
whether the moving target derived in the current target deriving
process of the radar apparatus 1 has been classified as the ACC
object in the classifying process of STEP S113 of the previous
target deriving process. In other words, the signal processing unit
17 determines whether the moving target has been classified as the
ACC object in the classifying process of the previous target
deriving process, with respect to the target data of the past
corresponding pair data derived in the current target deriving
process. Then, in a case of determining that the moving target has
not been classified as the ACC object (No in STEP S303), the signal
processing unit 17 proceeds to the process of STEP S304. Meanwhile,
in a case of determining that the moving target has been classified
as the ACC object (Yes in STEP S303), the signal processing unit 17
proceeds to the process of STEP S309.
[0119] In STEP S304, the signal processing unit 17 determines
whether the lateral distance of the moving target in the current
target deriving process is a predetermined distance or more (for
example, 2.8 m or more). In a case of determining that the lateral
distance of the moving target is the predetermined distance or more
(Yes in STEP S304), the signal processing unit 17 proceeds to the
process of STEP S305. Meanwhile, in a case of determining that the
lateral distance of the moving target is less than the
predetermined distance (No in STEP S304), the signal processing
unit 17 proceeds to the process of STEP S309. Like this, in the
determining processes of STEPS S302 to S304, it is determined
whether the moving target exists in the specific range on the
opposite side of the shelter Re, which is a continuing stationary
target, with respect to the position of the vehicle 100.
[0120] Now, the determination on whether the moving target exists
in the specific range on the opposite side of the stationary target
with respect to the vehicle 100 will be described with reference to
FIG. 13. FIG. 13 is a view illustrating the specific range in the
multi-path movement target determining process. From the scan range
SC of the vehicle 100 of FIG. 13, the moving target pc has been
derived. Also, the moving target pc has been already determined as
a moving target in the determining process of STEP S109. Next, the
signal processing unit 17 determines whether the moving target pc
is an object of the leading vehicle, that is, whether the moving
target pc exists in the range of the leading-vehicle determination
range pr (corresponding to STEP S302 of FIG. 11). The
leading-vehicle determination range pr becomes a range in which the
longitudinal distance from the position of the radar apparatus 1 of
the vehicle 100 is a longitudinal distance L11 (for example, 120 m
or less), the lateral distance from the position of the radar
apparatus 1 of the vehicle 100 in the left direction relative to
the vehicle traveling direction is a lateral distance S11 (for
example, 5.4 m or less), and the lateral distance from the position
of the radar apparatus 1 in the right direction relative to the
vehicle traveling direction is a lateral distance S12 (for example,
5.4 m or less). Here, the moving target pc exists in the
leading-vehicle determination range pr.
[0121] Next, the signal processing unit 17 determines whether the
moving target pc is an ACC object, that is, whether the moving
target pc exists in front of the vehicle 100 in the lane ro1 in
which the vehicle 100 is traveling (corresponding to STEP S303 of
FIG. 11). The range for classification as the ACC object is a range
in front of the vehicle 100 on the lane ro1. Specifically, the
range for classification as the ACC object becomes a range in which
the longitudinal distance from the position of the radar apparatus
1 of the vehicle 100 is less than 120 m or less, the lateral
distance in the left direction from the position of the radar
apparatus 1 of the vehicle 100 is less than 1.8 m, and the lateral
distance in the right direction from the position of the radar
apparatus 1 of the vehicle 100 is less than 1.8 m.
[0122] In addition to the range for classification as the ACC
object, there are a specific range Lt and a specific range Rt on
the left and right of the vehicle 100, respectively, and the moving
target pc exists in the specific range Lt. Like this, in a case
where the moving target exists in any one of the specific range Lt
and the specific range Rt which are ranges in the leading-vehicle
determination range pr of the scan range SC of the radar apparatus
1 and out of the lane (the lane ro1) in which the vehicle 100 is
traveling, the signal processing unit 17 performs a process of
setting a reflecting range of STEP S306 to be described below.
[0123] Returning to FIG. 11, in STEP S305, the signal processing
unit 17 determines whether the vehicle speed of the vehicle 100 is
a predetermined speed or more (for example, 40 km/h or more) on the
basis of a signal input from the vehicle speed sensor 40. In a case
of determining that the vehicle speed of the vehicle 100 is the
predetermined speed or more (Yes in STEP S305), the signal
processing unit 17 proceeds to the process of STEP S306. Meanwhile,
in a case of determining that the vehicle speed of the vehicle 100
is less than the predetermined speed (No in STEP S305), the signal
processing unit 17 proceeds to the process of STEP S309. This
condition is set because in the case where the speed of the vehicle
100 is the predetermined speed or more, it becomes difficult to
perform the determining process.
[0124] In STEP S306, in order to confirm whether the moving target
pc is a target based on a multi-path reflected wave, the signal
processing unit 17 sets the reflecting range (for example, a
reflecting range qe shown in FIG. 14 to be described below) on the
basis of the position of the moving target pc.
[0125] Now, the setting of the reflecting range qe will be
described in detail with reference to FIG. 14. FIG. 14 is a view
illustrating the setting of the reflecting range qe corresponding
to the position of the moving target pc. The signal processing unit
17 performs the operation of a trigonometric function on the basis
of the longitudinal distance L2 and lateral distance S2 of the
moving target pc, thereby obtaining a distance L2a. Then, the
signal processing unit 17 derives a longitudinal center mpa which
is the center of the distance L2a. Also, the signal processing unit
17 derives a lateral center mpb which is the center of the lateral
distance S2. Then, the signal processing unit 17 derives a line
segment extending in the angle direction of the moving target pc
and connecting the moving target pc and the radar apparatus 1, and
the reflective point mp which is the intersection of the
longitudinal center mpa and the lateral center mpb. Next, the
signal processing unit 17 derives the reflecting range qe having a
longitudinal distance La (for example, 30 m) with the reflective
point mp as the center, and a lateral distance Sa (for example, 4
m) with the reflective point mp as the center.
[0126] Returning to FIG. 12, in STEP S307, the signal processing
unit 17 determines whether there exists any stationary target to be
a factor causing a multi-path reflected wave in the reflecting
range qe. Then, in a case of determining that there exists at least
one stationary target in the reflecting range qe (Yes in STEP
S307), the signal processing unit 17 proceeds to the process of
STEP S308. Meanwhile, in a case of determining that there exists no
stationary target in the reflecting range qe (No in STEP S307), the
signal processing unit 17 proceeds to the process of STEP S309. In
other words, the signal processing unit 17 performs a process of
determining whether there exists at least one stationary target in
a predetermined range (the reflecting range qe where there may be a
stationary target to be a factor causing the moving target pc based
on a multi-path reflected wave) corresponding to the specific
position where the moving target pc exists, between the position of
the vehicle 100 and the specific position. In this way, it is
possible to derive the accurate position information of the moving
target pc corresponding to the multi-path reflected wave. Also, a
stationary target exiting in the reflecting range qe is a portion
of the above-mentioned continuing stationary target.
[0127] In STEP S308, the signal processing unit 17 sets a
reflection target flag, which represents that there a continuing
stationary target exists next to the lane ro1 in which the vehicle
100 is traveling, and the moving target pc exists in the specific
range Lt, to an ON state, and records the reflection target flag
information in the memory 172.
[0128] Next, if determining that the process on all target data
which are objects of the multi-path movement target determining
process has been terminated (Yes in STEP S309), the signal
processing unit 17 terminates the multi-path movement target
determining process and proceeds to the process of STEP S204 of
FIG. 10. Meanwhile, if determining that the process on all object
target data has not bee terminated (No in STEP S309), the signal
processing unit 17 returns to the process of STEP S301, and
continues the multi-path movement target determining process.
[0129] <4-4. Position Information Changing Process>
[0130] Now, a process of changing the position information of a
moving target will be described with reference to FIG. 15. This
process to be now described is for changing the position
information of a moving target based on a multi-path reflected wave
to the original position of the moving target. FIG. 15 is a flow
chart of the position information changing process. In STEP S401,
the signal processing unit 17 determines whether information on any
moving target with a reflection target flag in an ON state has been
recorded in the memory 172.
[0131] Then, in a case of determining that information on a moving
target with a reflection target flag in an ON state has been
recorded in the memory 172 (Yes in STEP S401), the signal
processing unit 17 selects the moving target to be an object, and
proceeds to the process of STEP S402. Meanwhile, in a case of
determining that information on any moving target with a reflection
target flag in an ON state has not been recorded in the memory 172
(No in STEP S401), the signal processing unit 17 terminates the
position information changing process, and proceeds to the process
of STEP S205 of FIG. 10.
[0132] In STEP S402, the signal processing unit 17 determines
whether the longitudinal distance of the moving target with the
reflection target flag in the ON state with respect to the vehicle
100 is in a predetermined longitudinal distance range (for example,
in a longitudinal distance range from 2.8 m to 5.4 m). Then, in a
case of determining that the longitudinal distance is in the
predetermined longitudinal distance range (Yes in STEP S402), the
signal processing unit 17 proceeds to the process of STEP S403.
Meanwhile, in a case of determining that the longitudinal distance
is not in the predetermined longitudinal distance range (No in STEP
S402), the signal processing unit 17 terminates the position
information changing process, and proceeds to the process of STEP
S205 of FIG. 10. Therefore, in a case of changing the position
information of a moving target, the changed position information of
the moving target becomes a position on the lane ro1 in which the
vehicle 100 is traveling. In other words, a moving target to be at
a position of the ACC object of the vehicle 100 by position
information change is set as an object of the position information
change.
[0133] Next, in STEP S403, the signal processing unit 17 subtracts
the lateral distance of the stationary target relative to the
vehicle 100 from the lateral distance of the moving target with the
reflection target flag in the ON state with respect to the vehicle
100, thereby deriving a lateral distance difference. This
derivation of the lateral distance difference will be described
below in detail.
[0134] Then, in a case of determining that the lateral distance
difference is a predetermined distance or more (for example, 1 m or
more) (Yes in STEP S404), the signal processing unit 17 proceeds to
the process of STEP S406. Meanwhile, in a case of determining that
the lateral distance difference is less than the predetermined
distance (for example, less than 1 m) (No in STEP S404), the signal
processing unit 17 proceeds to the process of STEP S405.
[0135] In STEP S405, the signal processing unit 17 performs a
process of adding a predetermined correlation value to the lateral
distance difference, thereby deriving a new lateral distance
difference. For example, in a case where the lateral distance
difference is 0.5 m, the signal processing unit 17 adds a
correlation value of 2 m to the lateral distance difference,
thereby setting the lateral distance difference to 2.5 m. In a case
where a difference correlation value is smaller than the width of
the shelter Re which is a stationary target, if the position
information changing process is performed on the moving target in
the next STEP S406, the position of the moving target becomes a
position on the stationary target. In order to prevent this, STEP
S405 is performed.
[0136] In STEP S406, on the basis of the lateral distance
difference, the signal processing unit 17 changes the position
information of the moving target with the reflection target flag in
the ON state. Specifically, the signal processing unit 17 changes
the position of the moving target with the reflection target flag
in the ON state to a position where the vehicle 100 is traveling,
the position obtained by folding back a specific position which is
the position of the moving target in the specific range Lt with the
continuing stationary target therebetween. In this way, it is
possible to derive the accurate position information of the moving
target.
[0137] Now, the lateral distance difference derivation and position
information change of the position information changing process
will be described in detail with reference to FIGS. 16 and 17. FIG.
16 is a view illustrating derivation of a lateral distance
difference S4. The signal processing unit 17 subtracts the lateral
distance S3 of the stationary target rp from the lateral distance
S2 of the moving target pc derived in the scan range SC of the
radar apparatus 1, thereby obtaining the difference. In other
words, the signal processing unit 17 derives the lateral distance
difference S4 of the moving target pc relative to the stationary
target rp. Then, the signal processing unit 17 uses the lateral
distance difference S4 to perform the process of changing the
position of the moving target. This process will be described in
detail with reference to FIG. 17.
[0138] FIG. 17 is a view illustrating changing of the position
information of the moving target pc. The signal processing unit 17
uses the position information of the moving target pc (the
longitudinal distance L2 and lateral distance S2 of the moving
target pc), the lateral distance difference S4, and the position
information of the stationary target rp (the longitudinal distance
L3 and lateral distance S3 of the stationary target rp) to change
the position information of the moving target pc to the position
corresponding to the moving target pb. In other words, the signal
processing unit 17 changes the position information of the moving
target pc to a position (the position of the moving target pb)
almost symmetrical to the specific position (the position of the
moving target pc) about a line segment ax extending in the
traveling direction of the vehicle 100 and including the stationary
target rp. As a result, the position information (the longitudinal
distance L2 and the lateral distance S2) of the moving target pc is
changed to position information (a longitudinal distance L5 and a
lateral distance S5) corresponding to the moving target pb. In this
way, it is possible to derive the accurate position information of
the moving target. Particularly, it is possible to derive the
accurate position information of the moving target existing at the
position symmetrical to the original position.
[0139] Here, a lateral distance S4 from the position (specific
position) of the moving target pc of FIG. 17 to the axis ax of
symmetry in the lateral direction and a lateral distance S4 from
the position of the moving target pb to the axis ax of symmetry in
the lateral direction are the same. However, they may be set to
different distances. Also, as shown in FIG. 17, the signal
processing unit 17 derives not only the stationary target rp but
also other stationary targets in the scan range SC. By doing like
this, the signal processing unit 17 derives a plurality of
stationary targets rg corresponding to the continuing stationary
target.
MODIFICATIONS
[0140] Although the embodiment of the present invention has been
described, the present invention is not limited to the
above-mentioned embodiment, but can be changed in various forms.
Hereinafter, these modifications will be described. All forms
including the forms described in the above-mentioned embodiment and
forms to be described below can be appropriately combined.
[0141] In the above-mentioned embodiment, the signal processing
unit 17 changes the position information (longitudinal distance and
lateral distance) of the moving target. However, the signal
processing unit 17 may also change relative speed information other
than the position information. Similarly to the changing of the
position information, the changing of the relative speed may be
performed by an operation using a trigonometric function.
[0142] Also, in the above-mentioned embodiment, in a case of
changing the position information of the moving target from the
specific position, the signal processing unit 17 changes the
position information to a position on the opposite side of the
stationary target rp with respect to the specific position on the
lane ro1 in which the vehicle is traveling. However, the changed
position on the opposite side of the continuing stationary target
with respect to the specific position may be a position on a lane
(for example, the neighboring lane ro2 or another lane) other than
the lane ro1.
[0143] Also, in the above-mentioned embodiment, the continuing
stationary target is an object having a certain length along the
traveling direction of the vehicle 100, for example, vehicles, the
inside wall of a tunnel, a guardrail, or the like continuing for 40
m or more at a side of the traveling direction of the vehicle 100,
and does not need necessarily to continue, and may be stationary
targets existing at regular intervals or at different
intervals.
[0144] Also, in the above-mentioned embodiment, in the
multiple-stationary target determining process of STEP S110, not
only the method of determining the number of peak signals but also
other determining methods may be used. Specifically, the signal
processing unit 17 may determine whether a moving target existing
at a specific position having the lateral distance larger than the
lateral distance of the continuing stationary target has been
derived a predetermined number of times or more by a plurality of
times of scanning, and in a case where a moving target existing at
a specific position having the lateral distance larger than the
lateral distance of the continuing stationary target has been
derived the predetermined number of times or more, the signal
processing unit 17 may determine that the determination condition
is satisfied.
[0145] Also, in the above-mentioned embodiment, as the conditions
of a case where the signal processing unit 17 changes the position
information of the moving target with the reflection target flag in
the ON state, in STEP S402, in a case where the lateral distance of
the moving target is in the predetermined lateral distance range,
one of the conditions to change the position information is
satisfied. However, the lateral distance of the moving target does
not need necessarily to be in the predetermined lateral distance
range. In other words, in a case of changing the position
information of the moving target, even if the changed position is,
for example, a position on the neighboring lane ro2 or a position
on another lane, not a position on the lane ro1 in which the
vehicle 100 is traveling, one of the conditions to change the
position information may be considered as being satisfied.
[0146] Also, in the above-mentioned embodiment, in a case where the
signal processing unit 17 derives the moving target at the position
of the moving target (for example, the moving target pc) based on
the multi-path reflected wave, not at the position of the moving
target (for example, the moving target pb) based on the direct
wave, the signal processing unit 17 changes the position
information of the moving target pc. Besides, in a case where the
signal processing unit 17 performs the target deriving process a
plurality of times, both of the moving target based on the direct
wave and the moving target whose position information based on the
multi-path reflected wave has been changed may be derived. In this
case, for example, the position information may be changed to the
sum of the individual position information items multiplied by
predetermined ratios. Specifically, the position information of the
moving target may be changed to the sum of the product of 0.9 and
the value of the position information of the moving target based on
the direct wave, and the product of 0.1 and the value of the
position information of the moving target to which the position
information based on the multi-path reflected wave has been
changed.
[0147] Further, in the plurality of target deriving processes, in a
case where the moving target based on the direct wave was derived
in the past (previous) deriving process, but is not derived in the
current deriving process, on the basis of the position information
derived in the prior deriving process, a process of predicting the
position information in the current deriving process (hereinafter,
referred to as an "extrapolating process") may be performed. Then,
in a case where, in one target deriving process, the signal
processing unit 17 derives the moving target based on the basis of
the direct wave by the extrapolating process, and the moving target
whose position information has been changed according to the
position information based on the multi-path reflected wave is also
derived, similarly to the case where the moving target of the
direct wave and the moving target whose position information has
been changed according to the position information based on the
multi-path reflected wave are derived, the position information may
be changed to the sum of the individual position information items
multiplied by predetermined ratios.
[0148] Specifically, by the extrapolating process, the position
information of the moving target may be changed to the sum of the
product of 0.6 and the value of the position information of the
moving target based on the direct wave derived and the product of
0.4 and the value of the position of the moving target whose
position information has been changed according to the position
information based on the multi-path reflected wave. Like this, in
the case of the extrapolating process, the ratio of the value of
the position of the moving target whose position information has
been changed according to the position information based on the
multi-path reflected wave may be increased as compared to the case
where the moving target based on the direct wave is derived.
[0149] Also, in the above-mentioned embodiment, the weighting on
the individual data items in the filtering of STEP S109 shown in
FIG. 8 is an example, and the weights may be values different from
those in the above-mentioned embodiment.
[0150] Also, in the above-mentioned embodiment, in a process such
as the multiple-stationary target determining process of STEP S110
or the multi-path movement target determining process of STEP S203,
the determination is performed by one target deriving process.
However, in a case where the determination condition is satisfied a
predetermined number of times or more by the plurality of target
deriving processes, only when all determination conditions of the
individual processes are cleared, the next process may be
performed.
[0151] Also, in the above-mentioned embodiment, as an example of
the method in which the signal processing unit 17 derives the
reflecting range qe, the method in which the signal processing unit
17 derives the line segment extending in the angle direction of the
moving target pc and connecting the moving target pc and the radar
apparatus 1, and the reflective point mp which is the intersection
of the longitudinal center mpa and the lateral center mpb, and
derives the predetermined reflecting range qe with the reflective
point mp as the center. However, the method of deriving the
reflecting range qe may be other methods, and if it is possible to
set a certain range including the reflective point mp, the signal
processing unit 17 may derive the reflecting range qe by other
methods.
[0152] Also, in the above-mentioned embodiment, the vehicle speed
sensor 40, the steering sensor 41, the brake 50, the throttle 51,
and the alarm unit 52 are provided outside the vehicle control
system 10. However, at least one unit of them may be provided
inside the vehicle control system 10.
[0153] Also, in the above-mentioned embodiment, the antenna scan
scheme of the radar apparatus 1 is a mega scan scheme. However, the
technology of the above-mentioned embodiment can be applied to an
electronic san scheme of using at least one algorithm of Digital
Beam Forming (DBF), Propagator method based on an Improved
Spatial-smoothing Matrix (PRISM), Multiple Signal Classification
(MUSIC), Estimation of Signal Parameters via Rotational Invariance
Techniques (ESPRIT), and the like to calculate the angle of a
reflective point of an object in estimating the direction of the
object without driving an antenna.
[0154] Also, in the above-mentioned embodiment, the transmission
wave and the reception wave which are transmitted and received by a
flat panel antenna fa are signals such as electric waves, laser
beams, or ultrasonic waves. However, the transmission wave may be
any other signal which can be transmitted from the flat panel
antenna fa, rebound from an object, and be received as a reflected
wave, thereby making it possible to detect the reflective point of
the object.
[0155] Also, in the above-mentioned embodiment, the antenna is the
flat panel antenna fa. However, the antenna may be any other
antenna such as a lens antenna or a reflector antenna capable of
transmitting a transmission wave and receiving the reflected wave
of the transmission wave from an object. Further, instead of the
transmitting antennae 13 and the receiving antennae 14,
bidirectional antennae capable of performing both of transmission
and reception may be used.
[0156] Also, in the above-mentioned embodiment, the radar apparatus
1 may be mounted on a vehicle, and may also be used for many
purposes (for example, at least one of monitoring of an aircraft in
flight and monitoring of a ship under way).
* * * * *